Nowadays, inverter devices that include multi-level inverters are widely used in inverter motors and power conditioners of solar power generation systems (e.g., patent document 1). In particular, a three-level inverter uses switching elements having a lower withstand voltage than those of a two-level inverter.
A three-level inverter includes four switching elements, which are connected in series, and two clamping diodes, which are connected in series. The series circuit of the four switching elements is connected in parallel to two capacitors, which are connected in series and divide the voltage of a DC power supply. Among the four switching elements, the two switching elements at the positive electrode side are referred to as switching elements of an upper arm, and the two switching elements at the negative electrode side are referred to as switching elements of a lower arm.
A connection point of the two clamping diodes is connected to a connection point of the two capacitors. A cathode terminal of the positive electrode side clamping diode is connected to a connection point of the two switching elements in the upper arm. An anode terminal of the negative electrode side clamping diode is connected to a connection point of the two switching elements in the lower arm.
The four switching elements are switched on and off so that the inverter device generates three levels of output voltages at a connection point of the upper arm and the lower arm.
An inverter device including two three-level inverters that are connected in parallel has also been proposed. The inverter device supplies a filter circuit with two three-level output voltages that are output from a connection point of an upper arm and a lower arm of the two three-level inverters. Then, the filter circuit combines the two three-level output voltages to form a sine wave.